The present invention relates to a drilling device having a radially displacable drill shank.
A drilling device is known having a drill bit chuck from which a drill bit having a front end abrasive face projects axially and which is driven by a drill shank. The drill bit of this drilling device and/or the panel in which a hole is to be made is arranged to be displaced radially with respect to a center line of the drill shank.
To produce drilled holes with an undercut, drilling devices are known which have as the drilling tool a drill bit having a drill head that widens towards the free end. The undercut at the bottom of the drilled hole is produced by displacing the drill head laterally by a swivelling motion or a gyratory motion. As this is happening, the undercut is reamed out in the area of the bottom of the drilled hole by lateral cutting edges or a lateral abrasive coating on the drill head. In order to produce not only the undercut but also the cylindrical part of the bore using such a drill head, the drill head is provided on its front end face with an abrasive coating, for example, of diamond chips. If it is desired to use this type of drill bit to produce the cylindrical part of the drilled hole in a facing panel, the entire front end face of the drilling head comes into engagement with the hard material of the facing panel. Because of the low cutting speed at the center of the front end face of the drill head, drilling has to be carried out with a high applied pressure, which leads to premature wear and blunting of the diamond chips. The service life of the drilling tool is consequently considerably reduced.
German Published Patent Application DE-A1 41 19 350 discloses a drilling device for producing drilled holes with an undercut in facing panels. The drilling machine disclosed therein, and thus also the drill bit attached thereto, is used for producing the undercut. To produce the undercut the drill bit is displaced away from the center line and is positively guided along a cam plate during the reaming-out operation. Swivelling is effected by hand and for that reason only a comparatively low speed gyratory movement of the drill bit is used during the reaming-out operation.